The over-the-counter market is used to trade securities that are not listed on an organized stock exchange. Trades are conducted either over the phone or electronically, and are governed by rules laid down by the Financial Industry Regulatory Authority. The group supporting this market is dealers who are willing to buy or sell securities for their own accounts, making a profit on the difference between the quote and bid prices for the securities in which they specialize. This market is decentralized, with geographically dispersed dealers. The prices at which trades are conducted can be kept hidden from others, so this market is not as price-transparent as a more traditional stock exchange.

The over-the-counter market represents the largest dollar amount of trading volume in the United States.